Ricerc@Sapienza

In this work, we report that 2-cyano-2-phenylpropanoic acid and its p-Cl, p-CH3 and p-OCH3 derivatives can be used as chemical fuels to control the geometry of the calix[4]arene scaffold in its cone conformation. It is shown that, under the action of the fuel, the cone calix[4]arene platform assumes a “locked” shape with two opposite aromatic rings strongly convergent and the other two strongly divergent (“pinched cone” conformation). Only when the fuel is exhausted, the cone calix[4]arene scaffold returns to its resting, “unlocked” shape.

Back and forth motions of the acid–base-operated molecular switch 1 are photo-controlled by irradiation of a solution, which also contains the photolabile pre-fuel 4. The photo-stimulated deprotection of the pre-fuel produces controlled amounts of acid 2, the base-promoted decarboxylation of which fuels the back and forth motions of the Sauvage-type [2]-catenane-based molecular switch. Because switch 1 and pre-fuel 4 do not interact in the absence of irradiation, an excess of the latter with respect to 1 can be added to the solution from the beginning.